Fastness of the color of a dye is tested by using a blue scale (blue standard dyed cloth) for dyed objects, painted articles, colored plastics, colored sashes, etc., and for measuring discoloration and fading of a sample as a result of said testing for fastness. The tested sample has been judged visually using a grey scale as specified in JIS L 0804 for discoloration and fading.
Also for measuring the degree of staining, such as fastness of color when subjected to washing, etc., the tested sample has been visually judged by using a grey scale specified in JIS L 0805.
This method of visually measuring the degree of discoloration and fading or the degree of staining of a sample by using a grey scale has been adopted internationally by such organizations as ISO, AATCC, ASTM, DIN, and BS, and this grey scale is specified as an international scale standard.
The conventional grey scale for measuring color fastness is not colored. It is constituted as shown in FIG. 3, with the first patch of each pair having a luminous reflectance value Y of 12% plus or minus a small deviation, and the second patch of each pair having the same or a successively higher value, as shown in FIG. 3.
The patches in the grey scale have differences in values of color E of 0, 1.5, 3, 6, and 12 respectively.
The grey scale for measuring the degree of staining is also not colored, similar to the grey scale for discoloration and fading. It is constituted as shown in FIG. 4, with the one patches having a luminous reflectance value Y of 85% and the other patches having differences in the values of color E of 0, 4, 8, 16, and 32 respectively.
The technical materials regarding the grey scales have included JIS L 0804 Grey Scale for Discoloration and Fading, JIS L 0805 Grey Scale for staining, JIS L 0841 Method of Testing Fastness of Dyeing against daylight, ISO 105-A02 Grey Scale for Assessing Change in Color, ISO 105-A03 Grey Scale for Assessing Staining, etc.
However, there are problems in the use of these scales.
Colored products, such as dyed articles, painted objects, colored plastics, colored sashes, etc. have various Y values ranging from a bright color to a dark color.
The conventional measurement of samples of those objects for discoloration and fading has been visually judged by comparing such samples having a plurality of pairs of patches, one of each pair having only one grey scale with a Y value of 12%, regardless of the color of the sample. The judgement is difficult and it takes time to make such a judgement, and there have been disadvantages such as low accuracy of the judgements.
In the judgement of the degree of staining, there have been problems similar to those in the measurement of discoloration and fading, and furthermore not only is staining of white fabric by washing or sweat a problem, but also staining of cloth of light and bright colors is a problem, and judgement of the degree of such staining depends on only one grey scale having a Y value of 85%. The judgement of the degree of staining have resulted in problems similar to those involved in the judgement of discoloration and fading.
For example in measuring discoloration and fading of a sample with a Y of 35%, the sample is compared with one dark grey scale with a Y of 12%, and the person who makes the judgement may doubt his judgement, he may require a long time to reach judgement, and also he may make a wrong judgement.
In order to make the judgement quick and precise, it is by all means necessary to avoid human error, and for this purpose it is necessary to determine if there is a difference in the visual acuity of the persons who make such judgements.
However, with the conventional grey scale it has not been possible to determine the visual acuity of the persons who make the judgements.